The present invention relates to a failure restoration method in a mesh network for automatically re-routing the traffic for restoration when a failure occurs in a node or a transmission line in a network having a plurality of nodes connected by transmission lines.
As shown in "Bellcore TA-NWT-001230, Issue 3", a method to restore the traffic transmitted over a transmission line, when a failure occurs in a single ring type network by re-routing the affected traffic toward the opposite direction against the failure has been known (hereinafter referred to as prior art method 1). This is a restoration method in the ring type network which consists of a plurality of nodes connected in ring with equal capacity lines and the capacity is divided into two, one half being for working capacity and the other half being for spare capacity, the traffic is normally transmitted by using only the working capacity; when a failure occurs, the spare capacity is used to loop back the traffic in the opposite direction against the normal direction to restore the affected traffic. Namely, the node which detects the failure loops back the traffic, which is output to the affected line, in the opposite direction by using the spare capacity (hereinafter referred to as bridging). Further, the traffic which was received from the working capacity at the location of the occurrence of the failure in the normal state is received from the spare capacity in the opposite direction and it is connected to the working capacity (hereinafter referred to as switching). In this manner, the restoration is achieved in the single ring type network.
In an alternative method, as shown in "GLOBECOM'87 28.2 THE SELFHEALING NETWORK", failure detecting nodes in a mesh network exchange messages and search for an alternate route or a restoration route for restoration (hereinafter referred to as prior art method 2). In this method, one of the failure detecting nodes sends out the message to all adjacent nodes. The contents of the message are 1) a sending node number, 2) a destination node number and 3) a capacity required for the restoration. When a node receives this message, it checks a vacant capacity in the line of the node and simultaneously outputs the message to all output lines which can secure the capacity required for the restoration. By this control, the message passes through a plurality of routes and reaches the other end node. The route through which the first arrived message has passed is adopted for the restoration route. In this manner, the restoration route is searched and the restoration is achieved in the mesh type network.
The prior art method 1, however, cannot be applied to the mesh network and an applicable field is restricted. The prior art method 2 is applicable for mesh networks, however it takes longer time to process. It also has a defect in that it lacks robustness.